The role of PMI in MFE/IFE common research

Transcription

1 The role of PMI in MFE/IFE common research Presented by Doerner for the Team and TITAN 1-1 Participants

2 In 2006, Jupiter II recognized that PMI was a bridge issue between MFE and IFE R&D Both MFE and IFE systems are subjected to transient power deposition events ITER ELMs are now limited to 0.5 MJ/m2, due to unacceptable melting/cracking of W & C at higher energy density IFE chamber loads of 0.1 MJ/m2 [ Raffray, JNM (2003)23] PMI effects may further limit it the allowable maximum energy level

3 Interaction with mixed-material surfaces in both IFE & MFE designs need to be included d Plasma-facing surfaces will interact Debris impinging i i of chamber wall will with condensable impurities interact with power deposition from deposited during steady-state MFE subsequent IFE shots operation Non-condensable impurities, such as He ash, and radiating species (Ar, Ne, etc) also alter PMI during subsequent MFE operation Neutron damage will also (hopefully) become significant and will change PMI Debris ion spectra from NRL154 MJ direct drive target [ Raffray, JNM (2003)23] The response of these resulting real, mixed-material surfaces to power transient events needs to be understood

4 Mixed-Material, transient surface heating and dpa effects R&D are underway in TITAN Response of surfaces exposed to simultaneous plasma and heat pulses Surface evolution of W in the presence of He ion bombardment Simulated neutron damage effects on fuel retention (Exposure of ORNL activated samples to plasma in TPE at Idaho Nat. Lab. is now beginning, Task 2-1)

5 Two laser systems exist at to investigate simultaneous laser and plasma irradiation Q-Switched Nd:YAG Laser 1064nm <850 mj ~5 nsec pulse <1 mrad Presently being used on -A Developing safety systems Debugging delivery optics Diagnostic development Can double as diagnostic beam Long-pulse Laser System msec pulse E pulse = J Up to 50 MJ/m 2 -sec 1/2 Fiber Delivery Available Installed into -A and -B Safety systems are incorporated into the -B Beenclosureenclosure Operational in -B since Jan. 09

6 MPLE SA Effects of D Loading on W Surface Damage Fluence to F = 5 x /m 2 surface before laser pulse varied F=5 x /m 2 F = 2 x /m 2 Absorbed Energy Impact ~45 MJ/m 2 s 1/2 (R W (λ=1064nm) ~ 70%) V bias = -125V Γ=2x10 22 /m 2 -sec T e =11eV n e =2x10 24 /m 3 T s ~ 50 C

7 Bulk sample temperature effects material loss rate during simultaneous plasma and heat pulses 0.8 Loss (mg) Differential Mass C Bulk 630C Bulk Ion Energy (ev) Increased mass loss rate correlates well with the amount of deuterium retained in the near surface region (~0.5 microns) that is heated during laser pulse

8 Surface morphology changes during repetitive surface heat loading and plasma exposure 25J 5msec Laser Hz (5 kw 50MJ/m 2 s 1/2 ) 75V Bias Total Fluence ~10 26 D + /m 2 Room Temperature ~550ºC

9 In a fusion environment He ash will have an impact of fpmi To date the laser system are being used to understand the synergistic effects observed during heat pulses and pure D plasma exposure In parallel, the effects of mixed D/He plasma exposure in steady-state are being investigated Eventually, these two R&D tracks will merge into studies of transient heating of surfaces exposed to mixed D/He plasma

10 W Temperature & PMI are coupled ~ K ~ K > 2000 K -B: pure He plasma ld l NF 48 ((2008)) M.J. Baldwin et al, 1200 K, 4290 s, 2x1026 He+/m2, 25 ev He+ (a) Bright field image (under focused image) NAGDIS-II: pure He plasma N. Ohno et al., in IAEA-TM, Vienna, K, K s, s 3.5x10 3 5x10277 He+/m2, 11 ev He+ 10nm -A: D2-He plasma M. Miyamoto et al. NF (2009) K, 1000 s, 2.0x1024 He+/m2, 55 ev He+ Little morphology Occasional blisters NAGDIS-II: He plasma 100 nm (VPS W on C) (TEM) Surface morphology Evolving surface Nano-scale fuzz D. Nishijima et al. JNM (2004) Surface morphology Shallow depth Micro-scale Mi l

11 A small amount of He (5-20%) in deuterium plasma results in suppression of blisters on W Plasma exposure conditions : fluence 5e25 m -2, 300ºC, E ion ~ 55 ev, 20% He. [from M. Miyamoto et al., NF 49(2009)065035]

12 Mixed D/He plasma exposure creates nano-bubbles in the near surface of W and reduces D retention TEM image of nano voids TDS of mass 4, He and D 2 [from M. Miyamoto et al., NF 49(2009)065035]

13 Mixed D/He reduces D migration in W at low temperature C D+He 12/ E26 D/m2 no He 12/08 1E26 D/m2 no He 12/08 5E25 D/m2 no He 03/08 1E26 D/m2 no He 03/08 1E25 D/m2 [from W. Wampler and Doerner, NF 49 (2009) ] D/W date D Fluence D retained D/m D/m 2 12/ (+He) / / / / With He 1e21 D/m 2 ~ 3 mg/m Depth (microns) Addition of He to the D plasma reduced D retention by about a factor of 35. With He, D retention is mainly at the surface, whereas without He, D retention peaks ~ 1 micron beneath the surface.

14 Above 900 K, W fuzz occurs. F growth Fuzz th consumes W bulk b lk s, 1120 K 60 ev He+ -B pure He plasma ~4 ITER shots ~2g m-2 (fuzz) ~20 ITER shots ~3g m-2 (fuzz) ~50 ITER shots ~6g m-2 (fuzz) RN N s, s 1120 K 60 ev He+ -B pure He plasma RN s, s 1120 K 60 ev He+ -B pure He plasma RN

15 Layer growth kinetics are limited by a diffusion like process at high He flux. Observed t 1/2 growth proportionality. The thickness of the nano-structured layer, d, agrees well with <d>=(2kt) 1/2 10 Laye er thickness, d (µm) 5 T s =1320 K T s =1120 K r thickness (µ µm) Laye He Γ He + (m -2 s -1 ) t = 3600 s T s = 1120 K t 1/2 (s 1/2 ) For consistent PMI conditions layer growth shows two regions of interest: - Layer growth rate increases y g D 2 -He exponentially for He + fluxes up to ~ m -2 s Layer growth rate is optimal for He + fluxes above this

16 Fuzz is approx. 95% space SEM used to profile fuzz layer thickness over sample surface. Fuzz layer removed. Mass change (D m =0.87 mg ±1%). (µm) Cross sec ctional height nano-structured layer W bulk t = 3600 s E ion = 30 ev T s =1120 K He Distance from center of target (mm) Geometric vol. of fuzz layer Comp. w/ pure W, (ρ = x10 3 kgm -3 ), est. (7.8 x10-10 m 3 ±10%). fuzz layer is 94 % porous.

17 Neutron damage is being simulated by using a high h energy Si ion beam 12 MeV Si ions are used, creating ~7500 displacements/ion, up to 0.6 dpa at 2 microns Damaged W samples are exposed to 100 ev D plasma in -A at several temperatures NRA measures resulting D depth profile up to 3 microns D retention peaks at damage maxima Compliments TPE measurements on neutron-activated samples

18 NRA measurements confirm less D retention after exposure to mixed D/He plasma Pure D plasma Mixed D/(5%He) plasma [W. Wampler and Doerner, NF 49 (2009) ]

19 Basic PMI measurements are relevant to both IFE and MFE research Surface loss rates from: Hydrogen loaded materials Mixed-material surfaces Morphology that develops from plasma interactions Tritium retention and permeation Mixed-material surfaces Migration rate measurements in damaged & undamaged surfaces Accumulation rate during transient heating events